LanguageNegotiationSelected.php

<?php

namespace Drupal\language\Plugin\LanguageNegotiation;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\language\Attribute\LanguageNegotiation;
use Drupal\language\LanguageNegotiationMethodBase;
use Symfony\Component\HttpFoundation\Request;

/**
 * Class for identifying language from a selected language.
 */
class LanguageNegotiationSelected extends LanguageNegotiationMethodBase {
  
  /**
   * The language negotiation method id.
   */
  const METHOD_ID = 'language-selected';
  
  /**
   * {@inheritdoc}
   */
  public function getLangcode(?Request $request = NULL) {
    $langcode = NULL;
    if ($this->languageManager) {
      $langcode = $this->config
        ->get('language.negotiation')
        ->get('selected_langcode');
    }
    return $langcode;
  }

}